1. Field of the Invention
This invention generally relates to non-impact type printers, and, in particular, to an improved carriage assembly for use in ink jet printers.
2. Description of the Prior Art
Ink jet printers are well known in the art. In an ink jet printer, a carriage on which is mounted a nozzle head for projecting a series of ink droplets toward recording paper is provided in a reciprocatingly movable manner to traverse the width of recording paper. Usually, such a carriage assembly is mounted on a guide rail which extends in parallel with a platen roller around which record paper is placed. As the carriage assembly is driven to move along the guide rail from the home position determined at one end of the guide rail to the opposite end, ink droplets are projected and selectively deflected to be deposited on the record paper thereby forming desired characters or images thereon.
FIG. 1 illustrates a typical prior art carriage assembly for use in ink jet printers. As shown, it includes a carriage 3 which is mounted on a pair of guide rails 1,2 movably therealong. It is to be noted that provision is made of a platen roller for placement of record paper therearound to the right of the carriage assembly extending in parallel with the guide rails 1,2, though it is not specifically shown in FIG. 1. A nozzle head 4 provided with a nozzle member 5 is fixedly mounted on a holder plate 10 and it projects a series of ink droplets in a predetermined direction. Also fixedly mounted on the holder plate 10 in the downstream of the nozzle head 4 with respect to the direction of projection of ink droplets are a charging electrode 6 and a pair of deflecting electrodes 7, 7'. Thus, when the ink droplets are passed through the charging electrode 6, they come to bear charges and, therefore, they are selectively deflected as they pass through the gap between the deflecting electrodes 7,7' in which an electric field is produced. With such a structure, two modes of operation are feasible. That is, in one mode of operation, an image signal is supplied to the charging electrode 6 to change the amount of charges of individual droplets. In this case, a constant electric field is produced between the deflecting electrodes. On the other hand, the electric field produced between the deflecting electrodes 7,7' may be changed in accordance with an image signal with equally charging the ink droplets.
The trajectory of deflected ink droplets is shown by the reference numeral 9; whereas, the trajectory of non-deflected ink droplets is indicated by the reference numeral 9'. As shown, a gutter 8 is fixedly provided on the carriage 3 in the downstream of the deflection electrodes 7,7' such that it collects the non-deflected ink droplets. A bracket 3a extends upwardly from the top surface of the carriage 3 and the forward end of the holder plate 10 is pivoted to the bracket 3a at 11. The backward end portion of the holder plate 10 is provided with a hole through which an adjusting screw 12 extends. The head of the screw 12 is in engagement with the top surface of the holder plate 10 and its bottom portion is screwed into a threaded hole provided in the carriage 3. Also provided is a coil spring 12' which is loosely fitted onto the screw 12 between the carriage 3 and the holder plate 10 so that the holder plate 10 is normally pressed against the head of the screw 12.
In the above described prior art carriage assembly, the projecting direction may be adjusted in the vertical plane by turning the screw 12 clockwise or counter-clockwise over a required number of times. This allows to obtain a limited alignment between the elements fixedly mounted on the holder plate 10 and the gutter 8. It should, however, be noted that the prior art structure still requires a precise sidewise alignment at the time of manufacture since the projecting direction cannot be adjusted sidewise after manufacture. In this regard, a mist absorbing plate 13 provided with a slit 14 is usually desired to be mounted on the gutter 8 to prevent blurring of a printed image from occurring as shown in FIG. 2. In such a case, it is desirable to make the slit 14 smaller. However, this then requires a higher precision in alignment among the elements to be provided on the carriage 3. In particular, the projecting direction of ink droplets must be set with high accuracy. Otherwise, the ink droplets may strike the edges of the slit 14 when deflected substantially as shown in FIG. 2.
FIG. 3 shows a typical structure in cross section of the prior art deflecting stage including a pair of deflection electrodes arranged opposite to each other. As shown, a deflecting electrode 15 is fixed to a base plate 16 through a screw 17. Also fixed to the base plate 16 by means of a screw 19 is an angle-shaped support member 18 which, in turn, supports the other deflecting electrode 20 as fixed thereto by means of a screw 21. The deflecting electrodes 15 and 20 are oppositely arranged to define a predetermined gap therebetween as a part of the passage for the ink droplets. A voltage may be applied between the electrodes 15 and 20 so that an electric field is produced in the gap. The level of the voltage applied depends upon the size of the gap, but a voltage of 3.5 kV may be applied, for example, in the case where a constant electric field is desired in the gap.
However, at the beginning of the ink jet projection, a significant amount of mist or fine, satellite droplets are created, and they tend to be collected on the electrode 15 or 20 depending on the sign of their net charges. Some of these satellite droplets are also deposited on the support member 18 to form a leakage path between the electrodes 15 and 20. The formation of such a leakage path is disadvantageous because it effectively decreases the strength of the field produced in the gap.
As exemplified above, various disadvantages are found in the prior art carriage assembly for use in ink jet printers and there has been a need for the advent of an improved ink jet printer carriage assembly.